Electronic devices, such as integrated circuits, are used in a variety of products, from automobiles to microwaves to personal computers. Designing and fabricating integrated circuit devices typically involves many steps, known as a “design flow.” The particular steps of a design flow often are dependent upon the type of integrated circuit being designed, its complexity, the design team, and the integrated circuit fabricator or foundry that will manufacture the integrated circuit.
Several steps are common to most design flows. Initially, the specification for the new integrated circuit is transformed into a logical design. With this logical design, the circuit is described in terms of both the exchange of signals between hardware registers and the logical operations that are performed on those signals. The logical design normally employs a Hardware Design Language (HDL), such as the Very high speed integrated circuit Hardware Design Language (VHDL). The logical design is then analyzed, to confirm that the logic incorporated into the design will accurately perform the functions desired for the circuit. This analysis is referred to as verification.
After the accuracy of the logical design is confirmed, it is converted into a device design by synthesis software. The device design, which is typically in the form of a schematic or netlist, describes the specific electronic devices (such as transistors, resistors, and capacitors) that will be used in the circuit, along with their interconnections. The device design typically corresponds to the level of representation displayed in conventional circuit diagrams. Verification is generally performed at this stage as well.
Once the relationships between circuit devices have been established, the design is again transformed, this time into a physical design that describes specific geometric elements. This type of design often is referred to as a “layout” design. The geometric elements define the shapes that will be created in various materials to actually manufacture the circuit device components (e.g., contacts, gates, etc.) that make up the circuit design. While the geometric elements are typically polygons, other shapes, such as circular and elliptical shapes, also may be employed. These geometric elements may be custom designed, selected from a library of previously-created designs, or some combination of both. Geometric elements also are added to form the connection lines that will interconnect these circuit devices. Layout tools, such as Mentor Graphics' IC Station or Cadence's Virtuoso, are commonly used for both of these tasks.
After the layout design is finalized, the integrated circuit device can be manufactured from silicon wafers using a lithographic process. During lithographic processes, the geometric shapes mentioned above are formed on a base material (e.g. silicon). Those of ordinary skill in the art will appreciate that lithographic processes have certain limitations. That is, a particular lithographic process will typically be able to manufacture certain shapes having specific characteristics. For example, the minimum size of shapes may be limited, the minimum proximity of shapes to each pother may be limited, or other such characteristics.
As such, adjustments to the layout design are often made during the design process in order for the shapes represented in the layout design to conform to the required characteristics for the particular lithographic process in which the layout design is to be manufactured.